The present invention relates to a method of cleaning layers of earth that contain noxious material, including separating the noxious material on the spot from loosened earth particles with a cleaning medium that is introduced into the earth layers under high pressure, and further including removing the noxious material with the cleaning medium, which is returned at the surface of the ground.
The present invention also relates to an apparatus for cleaning layers of earth that contain noxious material via a cleaning medium that takes up the noxious material and is introduced into the layers of earth via a drilling tube, with the cleaning medium, possibly together with earth particles, being extracted by suction from the layers of earth and subsequently being processed, and with the drilling tube being provided at its bottom end with a drill bit, and slightly thereabove, with an outlet nozzle for the cleaning medium, which is under high pressure.
In many cases, the removal of noxious materials from layers of earth is impeded by the changing stratification of different earth layers having various mechanical and physical properties. In many cases, earth that is loaded with noxious material must therefore be excavated and cleaned beyond the actual excavation site. However, if in addition to changing ground structure, little space is available and the depths of the uncleaned ground are great, the costs for excavating the earth become disproportionately high due to extensive safety measures that have to be undertaken. In such cases, it is desirable to be able to clean the earth on the spot. For this purpose, among others, biological earth-cleaning processes are known; however, these processes can be used to only a limited extent, especially where the layers of earth change. In addition, the time required for biological cleaning processes extends over several vegetation seasons.
One known method for cleaning layers of earth that contain noxious material uses a drilling tube that comprises an inner tube, which guides the cleaning medium into the layers of earth, as well as an outer tube that surrounds the inner tube. The bottom end of the inner tube is provided with a drill bit above which is disposed an outlet nozzle for the cleaning medium, which is under high pressure. Above the outlet nozzle, the outer tube is sealed off relative to the inner tube and is provided near its bottom end with a suction opening for the cleaning medium that is loaded with noxious material. Via an annular space that is formed between the outer and inner tubes, the cleaning medium that is loaded with noxious material returns under the effect of a suction pump to the surface of the earth, where it is conveyed to a processing unit. The earth-cleaning process that can be carried out with the heretofore known apparatus is carried out either during lowering or during retraction of the rotating drilling tube. The cleaning medium that is supplied via the inner tube leaves the outlet nozzle under high pressure and horizontally enters the earth layer that is to be cleaned as a cutting stream or jet. In this manner, the particles of the ground are sprayed and washed, and noxious material is removed. Due to the advancing axial movement of the drilling tube, the layers of earth that are saturated with cleaning medium subsequently reach the effective range of the suction opening of the outer tube, from where they are conveyed to the surface of the earth for subsequent transfer to a processing unit.
A drawback of this heretofore known method is that the column of earth taken care of by the cleaning process can have a varying diameter, since depending upon the construction of the earth layer, the depth to which the cutting jet penetrates and the magnitude of the respectively cleaned area about the drilling tube vary. This can lead to an undesirable influence upon already-cleaned areas, or areas of the earth that are free of noxious material.
It is therefore an object of the present invention to provide a method and apparatus for cleaning layers of earth that contain noxious material, with this method and apparatus permitting a precise localization of the area of earth that is to be subjected to the respective cleaning process, and also assuring at any given time control over the progress of the boundary between areas of earth that have been cleaned and that still contain noxious material.